Thermal response of Ru electrodes in contact with $SiO2$ and Hf-based high-$k$ gate dielectrics

A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with $SiO2$ and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the $Ru∕SiO2$⁠, $Ru∕HfO2$⁠, and $Ru∕HfSiOx$ film systems were observed through cross-sectional high-resolution transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy with electron-energy-loss spectra, and energy dispersive x-ray spectra analysis. Ru interacted with $SiO2$⁠, but remained stable on $HfO2$ at $1000°C$⁠. The onset of $Ru∕SiO2$ interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a $900°C∕10-s$ anneal. The dependence of capacitor device degradation with decreasing $SiO2$ thickness suggests Ru diffuses through $SiO2$⁠, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on $Ru∕HfSiOx$ samples may be due to phase separation of $HfSiOx$ into $HfO2$ grains within a $SiO2$ matrix, suggesting that $SiO2$ provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the $Ru∕SiO2$ system at $1000°C$ is presented.